It’s perhaps
natural to think that our universe should be more or less the same in all
directions, once we average out the lumpiness of stars, galaxies, galactic
clusters, superclusters, etc.However, there’s a growing
body of evidence suggesting that this presumption is not true.There is now a strong suspicion that our universe may contain a gaping
“hole” located in the constellation Eridanus.This all
started several years ago with the observation that there was a pronounced “Cold
Spot” in the data from the Wilkinson Microwave Anisotropy Probe (WMAP) that
produced space-based measurements of the cosmic microwave background (CMB) left
behind about 400,000 years after the Big Bang.

Let’s start by reviewing
the cosmic microwave background.Shortly after the initial
Big Bang, when fast exponential inflation had stopped, our universe settled down
to a slower and steadier rate of expansion.As more space
became available to hold the energy in it, the universe cooled to a nearly
perfect “liquid plasma” saturated with energy, in which quarks and gluons
behaved as free particles.As the cooling progressed, the
gluons thinned out and the quarks clumped into composite mesons, protons, and
neutrons.For some reason that remains obscure, there was a
slight excess of protons and electrons over their antimatter equivalents
(antiprotons and positrons).During the high-density stages
of the early universe, nearly all of the antimatter particles paired off with
their matter counterparts to annihilate, leaving behind the surviving matter
particles and producing a universe populated almost exclusively by matter.The cooling universe was then a “soup” dominated by free electrons and
protons.In this environment, a photon of light, strongly
influenced by any encounter with a charged electron or proton, could travel only
a short distance without being absorbed or scattered by one of the free charged
particles.But as the cooling progressed, the negative
electrons and positive protons tended to pair off to make electrically neutral
hydrogen atoms. The free charged particles, which easily absorb photons, were
replaced by light-transparent neutral atoms.The murky black
“soup” of the early universe became crystal clear.

The photons of the early
universe had energies characteristic of the light emitted from a hot object (the
universe) at a temperature of about 2,900 K.(Here, K means
“kelvin” and specifies the absolute temperature in Celsius degrees above
absolute zero.)As long as the universe was murky black,
these photons were trapped by repeated emission and re-absorption.However, the transformation to a transparent universe released them from
this trap, and they became free photons.These liberated
photons have been traveling through the universe ever since, and we detect them
today as the cosmic microwave background radiation. However, as the universe
expands and space itself stretches, the wavelengths of these CMB photons were
also stretched until they are now microwave photons characteristic of a very
cold object with a temperature of 2.73 K instead of visible light photons
characteristic of a hot object with a temperature of 2,900 K.We observe these CMB photons today as microwaves emitted from a “surface”
that has not existed for the last 13 billion years.

There has been a recent
flurry of activity to sweep the sky and map the CMB photon intensity vs. angular
position on a fine scale.WMAP has produced such a mapping,
producing an orange-tinged bluish map has become well known in science articles
and book cover art (see the figure below).In a localized
area on the right and well below the map’s center there is a particularly cold
region, quite dark as compared to the blue, yellow, and orange regions of most
of the rest of the map.This region is called the “WMAP Cold
Spot”, and it lies in the river constellation Eridanus.

When a feature like this
is obvious to the naked eye, there is a fairly good chance that it is
significant.The question that is raised is whether the Cold
Spot is just an expected fluctuation in the intensity of the CMB, or whether it
is non-statistical and might be an indication of something particularly
interesting going on.The answer is that it is definitely
not a simple statistical fluctuation.A group working the
Physical Institute of Cantabria in Spain
and at Purdue
University
has carefully analyzed the WMPA data and has concluded that the Cold Spot is not
compatible with normal Gaussian fluctuations of the CMB.

Recently two groups, one
at the University of Minnesota and the other at Cavendish Labs in England and in
Lausanne, Switzerland, have carefully examined the data from the National Radio
Astronomy Very Large Array Sky Survey (NVSS), which looked at 82% of the sky
visible from the VLA in New Mexico and catalogued more than 1.8 million
individual radio sources.The groups studied this
extragalactic survey, looking for structure at the Cold Spot location.Both groups have found a sizable dip in source population and radio
brightness at just the location of the WMAP Cold Spot.

The implication of these
results is that the Cold Spot is not a characteristic of the CMB itself, but
instead it is a phenomenon that happens as the CMB photons pass through the
universe on the way to our detectors. The combined WMAP and NVSS data suggest
that along the line of sight to the Cold Spot, there is an enormous volume
containing almost no stars, galaxies, or gas.A physical
process called the integrated Sachs-Wolfe Effect, the gravitational wavelength
shift of photons as they pass through varying gravitational fields in an
expanding universe, is probably responsible for the cold spot.As photons of light fall into the gravity well of a massive object like a
galactic cluster, they gain energy and are blue-shifted.On
emerging from the gravity well, such photons would lose the energy gained,
except that, due to the accelerated expansion effect of the large quantity of
dark energy in the universe, there is a net repulsion acting and it is a bit
easier to get out of the gravity well, so that not all of the gained energy is
removed.The net result is that CMP photons that pass
through regions containing significant mass arrive at our detectors with a bit
more energy on the average than those passing through regions of the universe
that are relatively empty.Therefore, the CMB radiation
should appear cooler along a line of sight passing through a large “empty”
region.Ineffect, the CMB radiation is weighing the universe
along the various lines of sight.

Although sizable empty
regions of the universe have been observed before in deep-sky surveys, the
region that has produced the Cold Spot appears to be much larger.It appears to be an unusually large “supervoid”, perhaps 1000 times
larger than the largest empty regions previously detected. The Cold Spot
Supervoid is estimated to be around 6 to10 billion light years from the Earth,
at a red-shift factor of about z=1, and to have a diameter
of around one billion light years.It is perhaps worth
noting that no computer simulations of the formation and evolution of the
universe have ever predicted a void of such a size.

What could cause the
Cold Spot Supervoid?I have not seen any speculations in the
astrophysics literature as to its origin.The prevailing
view seems to be that if it is there, then “it just happened.”

However, since this is a
science-fiction magazine, let me indulge in a bit of SF-related speculation.Some years ago I recall having a discussion about negative mass objects
and cosmic voids with my good friend, the late Dr. Robert W. Forward.Bob Forward, for reasons that those familiar with his work will
understand, was interested in the possibility that large concentrations of
negative mass might exist in the universe.He noted that if
there happened to be an object somewhere in the universe, perhaps a natural
worm-hole mouth, that had a very large negative mass, then it would tend to
repel all of the positive mass in the region, pushing it far away and sweeping
out a large empty region in the universe.

Since we now know about
the dominant dark energy in the universe, we can now add to Bob Forward’s
speculation by noting that the integrated Sachs-Wolfe Effect would work
backwards for photons that were climbing the gravity “mountain” of a negative
mass object (the inverse of a gravity well) and would cool the photons passing
through a region dominated by negative mass.

We have learned from
general relativity that, given some quantity of negative mass, we could build
space-time metrics that allow one to do all sorts of cool SF-related faster than
light gymnastics.Therefore, if we need some negative mass
to construct wormholes, warp drives, Krasnikov tubes, and so on (see earlier AV
columns in this series), there is now a good place to look for it.Just get in your hypervelocity starship and head for the WMAP Cold Spot.

John Cramer's new book: a non-fiction
work describing his Transactional Interpretation of quantum mechanics, The
Quantum Handshake - Entanglement, Nonlocality, and Transactions,
(Springer, January-2016) is available for purchase online as a printed or eBook
at: http://www.springer.com/gp/book/9783319246406
.